Monday, April 29, 2013

Today
I was showing to one of my students all the weak points of a Pressure
gauge transmitter and that he should not use them in any case,
as he had 2 of them. When I put the transmitter under pressure, a small
amount of air was coming out of the overpressure valve on the top and 6
seconds later the all thing exploded...and cut my finger...lucky me
only the finger...could have been worth or imagine this happening
underwater! So why did this happen? well after having a close look at
the transmitter it seems that the humidity that gets trapped in a
regulator, and you will always have that...started corroding the battery
that leaked a bit and made the all transmitter corrode and probably the
over pressure valve not work correctly....and the result was obvious
that when I opened the valve and the pressure entered the first stage
and the transmitter it just blew into pieces! so moral of the story,
these transmiters are gadgets, dangerous and useless. I always say that
and will remain firm DONT USE THEM!

Saturday, April 27, 2013

Interested in knowing more about Deep Stop? here you can download a file with some interesting explanations. Enjoy :-)

Deep Stops

by Tom Steiner van den Ouweelen

As a
technical diver I am pretty sure that you heard about Deep Stops. Now how does
all this work?

First you
should know that deep stops have been actually mentioned by Paul-Bert in 1878, so
it’s not as new as many might think, I am sure that you all heard about
Paul-Bert, just in case to refresh you, he is the one that found out “the
Oxygen Toxicity” (CNS), referred to as the "Paul Bert effect". He has
shown that oxygen is toxic to insects, animals, mollusks, birds and other
animals. Deep stops are also commonly named PYLE stops from Richard Pyle.

The main
reason for doing a deep stop is to reduce the critical fast tissue tension and
help reduce the incidence of decompression sickness and the fatigue after a
dive that is a subclinical DCS.

Different
computers and dive organizations tell you to do deep stops at different depth
and for a length of 2 minutes.

The 2 minute
stop that you will do at the deep stop is the time that the body needs to make one
full blood circulationand this will
help reduce the fast tissue tension.

There are
different ways used to calculate your deep stops, some computers are using
fixed values for different depth, some will tell you to do a stop halfway your
depth some will tell you to stop at 80% of your max depth, some have preprinted
tables... anyway there are loads of ways to make a deep stop and I am not
saying here that they are not right.

What is
interesting is to know how they are calculated.

So if I take
the first example of the DAN, that recommends you to do a 2 minute deep stop at
halfway of your depth.

Example :

50 meters
depth = deep stop of 2 minutes at 25 meters

In this
example the GVE (Gas Volume Expansion) will be 70%.

Assuming
that the initial size of a bubble is 1 on the surface, at a depth of 50 meters
(6 bars) the size of the bubble will be 6 times smaller:

1/6 =
0.1666666666666667

You will add
70% on top of it and it will result as follow :

0.1666666666666667
+ 70% = 0.2833333333333333

Now you will
divide the initial size of 1 (that you have on the surface) by
0.2833333333333333

1/0.2833333333333333
= 3.529 bars

3.529 bars =
25 meters (rounded)

The Gas Volume
Expansion percentage will tell you where you will perform the stop. So if you
take a Suunto computer it works with a GVE of around 70%, a VR3 with a GVE of
around 57% etc… and that’s how they define their deep stops.

I have been
using the GVE (Gas Volume Expansion) system now for over 14 years but with a
lower GVE for all my technical dives, I use typically 35% GVE.

There are
some basic rules you should know, ascent speed from a deep dive is 9-10 meters
per minute maximum, your first deep stop is always done on your back gas and
not on your deco gas, why that? Well if you have been staying for a while at a
PPO2 of 1.4 your body needs to rest a while before switching to a higher PPO2
that will be 1.6, don’t forget your body is a pressure machine, so respect it
and listen to your body. Ascent time from your last deco stop to the surface 1
METER per minute.

A good
advice, in warm water a PPO2 for the bottom gas of 1.4 is fine, for deco gas
1.6, in cold water a PPO2 for the bottom gas of 1.2 is highly advisable and for
your deco gas use 1.4 PPO2.

Repeat the
Deep Stop as long as you are more than 10 meters from your first deco stop.

You can
round depth to your switch, if your second deep stop has to be done at 22
meters and your switch is at 21 meters,then you will just switch to your deco gas at 21 meters on your 50% mix,
just remember first deep stop is on the back gas.

Let’s take
an example with 1 deep stop and a gas switch at the deco stop.

Depth : 50
meters

GVE : 35%

First switch
at 21 meters on a 50% mix.

Second
switch at 6 meters on O2.

Now in this
example I will show you how you can do the calculation easier.

Just divide
the pressure, 50 m = 6 bars by 1.35 (one is the initial size and 35 is the GVE
that you decide to use)

6/1.35 =
4.44444444444444 bars that equals 34 meters

Now for the
second deep stop you will divide 4.44444444444444 by 1.35

And this
equals : 3.2921…bars that equals at 22 meters. In this case you will merge the
deep stop with the gas switch on your 50% mix, that will become the first deco
stop.

Now
regarding the GVE, you can use all types of GVE, from 20% up to 70% maximum,
that’s my advice. Now honestly the GVE that I would use depends on the type of
dive I plan, in good conditions, warm water, no current etc… I would use down
to 25%.

35% is the
one I use most and works out fine on most dives, in cold water I would rather
opt a higher GVE, 45% or 55% as I don’t want to hang to long in the shallow
stops due to the cold.

The point is
that if you stay deeper for longer time you will on gas your slow tissues while
you ascent so you need to find a value that suits you best and therefore you need
to try some values.

Never forget
that the deep stops have to be
integrated in your plan, and on some software’s you need to add the ascent
time as well between your maximum depth and your first or second deep stop.
Deep stops will also make your decompression time a bit longer at the end, but
you will feel better and less tired when you come out of the water.

I hope that
this document has been interesting for you and if you wish to receive the Deep
Stop generator feel free to contact me and I will email it to you. It’s a free
software that runs on windows.

Never forget
to seek proper training with an experienced technical instructor and when it
comes up to deco, start with it gently and don’t be too aggressive, build
Bottom time slowly up.

Wish you
some great technical dives.

Tom Steiner van den Ouweelen

Deep stops
should be taken to be experimental and should not be used without a full
understanding of the inherent risk of Decompression Sickness while diving.

No deep stops
of any sort can guarantee that DCS will NOT occur.

The only way
to avoid the risk of DCS is to stay on the surface and NOT DIVE.

The author of
this article will not be held accountable for any injury caused by the use of a
profile generated by this document or by the Software.